building construction 3 - Lecture 2

1. PLASTERING AND DRY LINING
Building Construction III
Spring 2012
Dr.Hikmat Hammad
Lecture 2

2. Learning outcomes
After Studying this chapter, students should be
able to:
• Identify the purpose of plastering in a building
• I identify the materials used in plasters
• Identify different types of plasters
• Identify the application procedure
• Identify the common problems in plasters
• Identify the application of dry lining

3. General
Plastering can be defined as the process of
covering rough surfaces with thin coat of
plastic material to form a smooth durable
and jointless surface.
• The coating of plastic material is termed
as “plaster”.
• The term plastering is usually called the
application to internal wall and ceiling
finishes.

4. • The application to the outside surface
which are subject to severe atmospheric
effects is known as “Rendering” or
“Stucco”
• The main binding agent in “Rendering” is
portland cement

10. The purpose of Plastering
Plastering and Rendering are applied to uneven
surface to achieve the following objectives:
• To protect the surface against atmospheric
effect such as sun, rain, snow, etc.
• To provide smooth, hygienic surface
• To conceal defects in the background and
provide decorative effect.
• To provide thermal insulation, sound insulation
and fire protection

11. • The plastering work is wet and messy
process and is greatly effected by the
weather conditions.
• The application is difficult, time-consuming
and costly.
• Nowadays in modern construction the
application of plastering is reduced and
replaced by various types of dry lining on
interior surfaces and cladding on exterior
surfaces.

12. • Exterior plastering (rendering) requires the
consideration of hazards such as water
penetration, frost effect, corrosion of steel
accessories placed in the plaster, stresses
induced due to wide variations of
temperature and humidity, wind and dust.
• Therefore, the plaster mixes and
application techniques on outside surface
should be different than interior
application.

13. • Since it is subject to direct wetting due to
rain, rendering requires cementitious
binding material such as Portland cement,
and the Masonry Cement.
• The use of lime alone as a binder has
been practiced in the past but now it is
used as an admixture to the cement to
improve workability.

14. Materials used in Plastering
• Plastering is the application of plastic
mortars on the hard rough surfaces.
• The plastic mortars are consist of a
binding material, aggregate, water and
certain admixtures to improve the quality.
• The binding materials used in the mortars
are Portland cement, masonry cement and
lime.

15. • Portland Cement: due to its strong binding
ability, normal Portland Cement is widely used
in plastering work.
• It is available natural gray or white color.
• White cement can be used in finishing coat with
colored aggregate to produce desired decorative
effect.
• For areas subject to sulphate attack “Sulphate
Resisting Cement” is recommended.
• In cold weather “high Early Strength Cement”
should be used.
• It can gain higher strength in the first few days
which minimizes the frost damage on the
plaster.

16. • Masonry Cement: it is manufactured from
normal Portland cement by the addition of
certain admixtures such as lime and air
entraining agents to increase the
workability.

17. • Lime: the use of lime alone in the plaster mix is
now rare. It is used as admixture
• Quicklime (CaO) is slaked by addition of water
and the excess water is drawn out to obtain
hydrated lime.
• Hydrated lime is added to the mortar during
mixing time.
• Lime may have some impurities from natural
source which effect the final properties.
• Magnesium, aluminum and Iron Oxides are
common impurities.
• Magnesium oxide in the lime produce highly
workable mixes but it takes longer time to
hydrate.

18. • Aggregate: the aggregates for plastering
are usually sand or lightweight aggregates
such as perlite and vermiculite.
• sand used in the plaster mixes can be
obtained from the rivers, from the sea or
by crushing stones.
• Aggregate constitutes the major part of the
mortar mixture by volume.
• Therefore, it is important that the
aggregate should be clean, sound and
well graded with particles ranging from fine
up to a maximum size.

19. • For undercoats coarser sands are used
then the finishing coats.
• Grading of sand is very important to fill the
voids between larger particles and smaller
particles.
• This increases the workability and reduces
the shrinkage of the mix.

20. • B.S.1191 gives three different
grading of sand to be used in
undercoats and finishing coat of
plaster.
Type IIType IB.S.Sieve
1001005.0 mm
90-10090-1002.36 mm No. 7
70-10070-1001.18mm No.25
40-8040-80600 µm No.25
5-505-40300 µm No.52
0-100-10150 µm No.100

21. • Water: water for mixing and curing should
be clean and free from harmful materials
such as oils, acids, alkalies, salts or
organic substances that could effect the
final quality of the work.
• Any drinkable water may be used for
mortar preparation.

22. • Admixture: certain type of admixture such
as asbestos, animal, vegetable or glass
fibbers as well as certain chemicals can be
added to the plaster mortars.
• These are generally added to undercoat
plasters to improve bonding to the
background.
• All admixtures should be free from dirt and
chemicals harmful to the mortar.